摘要:

Silicon carbide grown by the chemical vapor deposition process on silicon often contains high concentrations of nitrogen donors with a binding energy of 54 meV as determined from photoluminescence studies. In contrast, the conductivity in the same samples is dominated by a heavily compensated shallow donor with a binding energy below 20 meV. The conventional view is that these two donors are the same. The 54 meV donors usually are assumed to be isolated substitutional nitrogen in regions of low concentration while the <20 meV donors are believed to be nitrogen in regions of high concentration. The most convincing evidence for this identification is the continuum of binding energies from 50 to 15 meV for SiC as a function of donor concentration compiled from published results. Evidence for reassessing the conventional view is given in this article and several experiments supporting the conventional view are reconsidered. As a result of this reconsideration, we propose that the donors below 20 meV which dominate the conductivity are not neutral, substitutional nitrogen in high concentration but some other center.D−centers and donor complexes are possible origins of this donor. TheD−center appears to have many of the characteristics required for satisfactory modeling of this material.

ISSN:0021-8979    

DOI:10.1063/1.354785

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We examine the dynamics of electronic transitions into the shallow states of attractive impurity centers in GaAs through numerical simulations. The molecular dynamics based formulation circumvents the difficulty of having to evaluate ‘‘sticking functions,’’ enables accurate computations of the phase‐space distribution function, and allows microscopic treatment of both the carrier‐phonon and carrier‐carrier phenomena on an equal footing. Energy dependent trapping rates with and without the presence of external electric fields are obtained, and we consider situations involving both singly‐ and doubly‐charged impurity centers. We show that initial trapping is reduced as a result of free‐carrier screening, and hence detailed knowledge of both the trap density and the electronic concentration is necessary for a meaningful prediction of the trapping behavior. Finally, we also focus on modifications caused by electron‐electron scattering, and find trapping enhancements due to the additional energy loss channel created by Auger‐like phenomena.

ISSN:0021-8979    

DOI:10.1063/1.354786

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The results of an ensemble Monte Carlo simulation of the electron transport in gallium nitride (GaN) are presented. The calculation shows that intervalley electron transfer plays a dominant role in GaN in high electric fields leading to a strongly inverted electron distribution and to a large negative differential conductance. An analytic expression for the polar optical momentum relaxation time for phonon energies larger than the thermal energy is also derived. This expression applies to many wide‐gap semiconductors, such as GaN and SiC, at room temperature since these semiconductors have large polar optical‐phonon energies (on the order of 100 meV). The calculated mobility agrees well with the results of the Monte Carlo calculation.

ISSN:0021-8979    

DOI:10.1063/1.354787

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We present a theoretical investigation of the growth orientation dependence of valence‐subband structures in ZnSxSe1−x/ZnyMg1−ySzSe1−zquantum wells grown in the [001], [115], [113], [112], and [111] directions. The results indicate that the in‐plane effective mass of the heavy‐hole subband in the [111]‐oriented structure is substantially smaller than that in the [001] quantum wells. For applications to quantum‐well lasers, the lighter effective mass will lead to a smaller threshold current density, and therefore a better laser performance. Our investigations should provide useful guidelines for the design of II‐VI quantum‐well blue lasers.

ISSN:0021-8979    

DOI:10.1063/1.354788

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have performed an extensive series of measurements on symmetrical barrierbound‐to‐continuumand asymmetrical barrierbound‐to‐boundquantum well infrared photodetectors consisting of only asinglewell. We find that the behavior of the optical (e.g., responsivity) and transport properties (e.g., gain) as a function of bias is strikingly different from that of the usualmulti‐quantum well detectors. The simplicity of the structure has allowed an accurate theoretical calculation of the potential drops across each barrier, the photoinduced carrier depletion in the quantum well and therefore a detailed understanding of the device physics.

ISSN:0021-8979    

DOI:10.1063/1.354789

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We present a detailed analysis of the electronic carrier transport in silicon when subject to a nonuniform stress distribution. Such a distribution gives rise to two independent current components which can be viewed in terms of carrier generation‐recombination. One component arises as a result of the nonuniform stress induced position dependent density of states, and the other due to stress induced shifts in the band edges. The various parameters and coefficients describing these phenomena are presented.

ISSN:0021-8979    

DOI:10.1063/1.354790

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The saturation of light‐induced defect density in hydrogenated amorphous silicon (a‐Si:H) has been studied as a function of various material parameters, such as initial defect densityNinit, Urbach energyEu, hydrogen contentcH, hydrogenated void fractionR, and deposition‐induced annealable defect density &Dgr;Nann. These parameters were varied by depositing samples at various substrate temperatures or by postgrowth anneals of samples grown at low substrate temperatures. It is found that total defect density of saturated light‐soaked stateNsatis well correlated with theNinit,Eu,cH,R, and &Dgr;Nannin the as‐grown states but no correlations betweenNsatand parameters other than theNinit,Eu, and &Dgr;Nannin the annealed states are found. It is also observed that annealing before light soaking reduces theNsatsubstantially. In particular, it is found that the value ofNsatfrom the fully annealed state is much lower than that from the as‐grown state with similarNinitandEu. A possible parameter that plays a primary role in the saturation of light‐induced defects is discussed.

ISSN:0021-8979    

DOI:10.1063/1.354791

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We determine, by first‐passage‐time simulations, the effective conductivity tensor&sgr;eof anisotropic suspensions of aligned spheroidal inclusions with aspect ratiob/a. This is a versatile model of composite media, containing the special limiting cases of aligned disks (b/a=0), spheres(b/a=1), and aligned needles (b/a=∞), and may be employed to model aligned, long‐ and short‐fiber composites, anisotropic sandstones, certain laminates, and cracked media. Data for&sgr;eare obtained for prolate cases (b/a=2, 5, and 10) and oblate cases (b/a=0.1, 0.2, and 0.5) over a wide range of inclusion volume fractions and selected phase conductivities (includingsuperconductinginclusions andperfectlyinsulating‘‘voids’’). The data always lie within second‐order rigorous bounds on&sgr;edue to Willis [J. Mech. Phys. Solids25, 185 (1977)] for this model. We compare our data for prolate and oblate spheroids to our previously obtained data for spheres [J. Appl. Phys.69, 2280 (1991)].

ISSN:0021-8979    

DOI:10.1063/1.354792

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A time‐dependent Schro¨dinger equation has been solved numerically for a double‐barrier and a quantum‐well resonant tunnelling structure. Special emphasis has been paid to the system where barriers are doped specially by negative delta‐function potentials (&dgr; potentials) which broaden the widths of the resonances and in turn decrease the dwell times. The strengths of the delta functions could be such that they may form bound states in the barrier regions, but the states bound to &dgr; potentials are very shallow. Delta‐function potentials are replaced by equivalent barriers of different heights and widths which are easy to incorporate into the numerical calculation of the propagation of the wave packet, and the corresponding physical structures can be conveniently fabricated. It is found that for a certain strength of the &dgr; potential or parametric value of the equivalent barriers in the barriers of the resonant tunneling structure, there are three resonance states very close together. The square of the wave functions trapped in the well region for the states oscillates in time for a broad wave packet inkspace, whereas the wave function trapped in the whole structure decays exponentially. The oscillating part has a resemblance with the quantum beats. There are no oscillations for a narrow wave packet inkspace.

ISSN:0021-8979    

DOI:10.1063/1.354793

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The defect energy levels in metalorganic chemical vapor deposition (MOCVD) grown GaxIn1−xP/InP:Fe and GaxIn1−xP/InP:S epilayers (x≤0.24) have been studied by photoluminescence (PL) and photoconductivity (PC) measurements. To understand the origin of the observed deep levels, we have determined the temperature dependence of the intensity and half‐width of the dominant deep‐level PL peaks. We find that (1) the dominant deep‐level peaks of the samples grown on the same substrate are related to the epilayer composition, and move to higher energies with increasing gallium content; (2) the dominant deep‐level peaks of the samples with the same epilayer composition grown on different substrates are different. They are attributed to the impurity in the substrate diffusing into the epilayer during MOCVD growth, forming an impurity‐vacancy complex. The following tentative assignments are proposed: the dominant deep‐level peaks in GaxIn1−xP/InP:Fe and GaxIn1−xP/InP:S are attributed to the emission of a (V)P‐(Fe)IIIcomplex and a (V)III‐(S)Pcomplex, respectively. Comparing the deep level with the near‐band‐edge emission we show that (1) all deep levels are independent of the band edge asxis varied; (2) the composition dependences of the deep levels associated with such complexes depend on the site occupied by the impurity atom.

ISSN:0021-8979    

DOI:10.1063/1.354794

出版商:AIP    

年代:1993

数据来源: AIP